How to reach less than 15 kWh/m² in an office building

case studies
How to reach less than 15 kWh/m²
annual final energy use for HVAC
in an office building
J-C Léonard
EDF R&D – Energy in Buildings and Territories Department.
Site des Renardières. Avenue des Renardières – Ecuelles.
77818 Moret sur Loing CEDEX – France.
jean-christophe.leonard@edf.fr
P Pedrocchi
Image et Calcul. 11 rue Alfred de Vigny
25000 Besançon.
pp@image-calcul.fr
The activity of the HDL Company, located
heat pumps, distribution pumps, venti-
in Besançon (France), is to renovate build-
lation, lighting and others uses. We show
ings. HDL wanted to show its expertise in
the improvements made during these two
energy efficiency in the most credible pos-
first years of operation. Finally, to general-
sible way: by applying it to its new head-
ize this field case to other refurbishment
quarters. In 2008, HDL refurbished an old
operations, we propose eleven rules to be
school (2 036 m²) to establish its new of-
applied to achieve this level of consump-
fices. HDL wanted an exemplary opera-
tion. So far and according to our informa-
tion: reach less than 15 kWh (final ener-
tion, this renovation operation remains
gy)/m².year for HVAC consumptions. EDF
the most efficient one in France.
offered them support by measuring the site energy performance.
In this article, we describe the technical characteristics of the building and the HVAC systems in place.
Then, for each end-use, we present
two years of energy and performance measurements: ground source
Building
Habitat Développement Local (HDL) has
acquired the former school Jean-Jaurès
(2 036 m²) in Besançon (Figure 1) and completed a partial expansion to install offices and
40
REHVA Journal – January 2012
Figure 1. HDL’s Headquarters.
case studies
Figure 2. Chilled beam during installation.
Figure 3. AHU with rotary exchanger.
create a central building housing the various departmental structures of Habitat. The activity of the company includes renovating and leasing out buildings. Concerned
by sustainable development, HDL wanted to show its
clients how to master energy efficiency in the most credible possible way: leading by example.
The consultants Image & Calcul, based in Besançon,
were entrusted with the task of rehabilitating the site
with an ambitious goal: to keep consumption under 50 kWhEp/m².year (Ep: primary energy) for the
Heating, Ventilation and Air Conditioning (HVAC)
in a region known for its harsh winters (temperature of
–13°C) and its hot summers. A high level of energy efficiency was required in terms of energy efficiency.
Minimizing all requirements: heating,
cooling and lighting
Losses under base conditions are 65 kW, or 32 W/m².
Reinforced insulation in opaque walls –part of the insulation is made from the outside– results in U coefficients around 0.25 W/m².K. In addition to 20 cm of
mineral wool, roof insulation is completed with 8 cm
of wood wool (U: 0.14 W/m².K). Here the goal is to
reinforce thermal inertia in the roof for comfort in summer. Indeed, in addition to its low thermal conductivity,
wood wool benefits from high mass density and thermal
capacity. In summer, the heat coming from the roof is
therefore delayed by 5 to 7 hours, after employees have
left the offices.
Windows are aluminum with argon-filled double glazing (Uw: 2 W/m².K). The surface area is limited, covering 28% of the façade on average. This type of glazing is a good compromise between a low solar factor
(38%) to limit solar contribution and high light transmission (70%) to promote natural lighting. The upper part of the interior office walls have translucent
panels that allow light to pass through to the central
walkways. To minimize energy consumption due to
lighting, motion detectors were installed in all walkways and service areas. They also control HVAC in
meeting rooms.
Installing high efficiency equipment
Distribution terminals are chilled beam modules
(Figure 2). These are cassettes without fans that require
neither filters nor condensation trays. Maintenance is
therefore quite simple. These cassettes are operating at
high temperature in summer (17°C) and low temperature in winter (35°C). Pretreated air in the central unit
is brought into the beams via buses that pass the air over
the batteries by induction.
Losses related to air renewal are minimized: Air
Handle Unit (AHU) is equipped with a high efficiency rotary heat exchanger with 80% efficiency
(Figure 3). The two fans are equipped with variable
speed drive. Hygroscopic coating on the recuperator
humidifies new air in the winter and dries it in the
summer.
REHVA Journal – January 2012
41
case studies
Figure 4. Water/water heat pumps.
Hot and cold water are produced by two glycol/water
heat pumps (Figure 4). The heating power of each is
32.6 kW, cooling power is 25.4 kW for absorbed power
of 7.2 kW (COP of 4.5 at 0°C/35°C). A 9 kW electric
heater is installed on the loop in order to prevent imperfection in implementation of insulation in the rehabilitation. Heat pumps are connected to a field of ten
vertical geothermal probes, each penetrating to a depth
of 100 meters (Figure 5). The size of the field was based
on 50 W/ml. In winter, water coming from the probes
travels to the heat pump evaporators. In summer, priority is given to the geo-cooling mode: water from the
probes supplies the cooling battery of the AHU and the
comfort modules, via a heat exchanger. In this case, the
building is cooled without electric compression.
In case of heat wave, the heat pump supports the geocooling mode. The schematic diagram allows possible heat evacuation from the heat pump condenser to
the vertical probes. Most of the circulation pumps are
equipped with variable speed drive.
Finally, in addition to motion detectors, T5 type lighting is used. The cost of HVAC part, with the vertical
geothermal probes, was 194 €HT/m².
Remarkable result
Final consumptions for all uses reach 50.1 kWh/m².year.
HVAC consumptions represented less than a third with
14.5 kWh/m².year (or 37.5 kWhEp). HDL has improved the set goal (50 kWhEp/m².year) despite a harsh
winter. Other uses represent two thirds of consumption,
or 36 kWh/m².year, ten of which are related to lighting
(Figure 6).
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REHVA Journal – January 2012
Figure 5. Geothermal probes.
100% = 50.1 kWh/m².year
Pumps
1,7 kWh/m 2
3%
Computers,
etc...
2
25.6 kWh/m
51%
AHU
3,4 kWh/m 2
7%
Heat pumps
9,4 kWh/m 2
19%
Light
10 kWh/m 2
20%
Figure 6. Distribution of annual consumption by use.
Heat pumps are operating under excellent conditions:
their average annual COP machine is 4.2 and close to
4 when including consumption of the pump that irrigates the geothermal probes. Despite the cold weather
during the winter of 2009–2010, electric output was
never required. Geo-cooling was able to provide necessary cooling (Figure 7).
Table 1 shows the changes of consumption rate between
the first and the second year of operation. The improvements come from better settings, especially concerning
programming intermittency, detection of air flow leaks
in ventilation pipes, cleaning clogged pump filters, lowering condenser temperature, etc.
case studies
3200
3200
2 000
5,0
6 000
4,0
4 000
3,0
GeoͲcooling
GeoͲcooling
2,0
2 000
1,0
0
0
0,0
Others
Others
4,0
Heat pumps
Heat pumps
AHU
AHU
Pumps
COP
Pumps
COP
3,0
First year
"First
commissioning"
2,5
4,8
12,5
19,8
37,8
Second year
"Refinement
settings"
1,7
3,4
9,4
14,5
35,6
Total
57,6
50,1
Heating needs
Cooling needs
COP*
Degrees days
(Average thirty 2555)
52
3
3,8
2594
43
6
4,15
2486
Consumptions by use
2,0 Pumps
AHU
1,0 Heat pumps
0,0 HVAC
Others
Figure 7. Monthly changes by uses and COP of the
heat-pump.
“Class A” in terms of greenhouse gas
emissions
When including lighting consumption, this site reaches
a class B energy label, and class A in terms of greenhouse
gas emissions. A gas boiler and air/water cooling unit
solution (performance estimated at 95%) would have
been positioned in class B also, but in class B concerning greenhouse gases emissions. The vertical geothermal
solution reduces CO2 emissions by two-thirds.
Competitive operating budget
Geothermic solutions have a clear advantage over fossil fuels in terms of operating costs: MWh of heat from
the heat pumps is around 28 € Tax Free/MWh (set premium included, the site has a “yellow tariff ” for electricity). With a gas boiler, it would have been close to 45 €
Tax Free/MWh. Under these conditions, the costs of the
energy station are particularly low, reaching 5.6 €/m²,
all uses included. The HVAC annual cost represents
1.9 €/m² with 1.3 for the heat pumps. It’s remarkable.
This operation shows that geothermic solutions are an
excellent source of eco-efficient energy.
It has allowed HDL, with the involvement of all players, to achieve its ambitious target. Two bars that are
difficult to achieve, in primary energy, were passed:
40 kWhEp/m².year for HVAC and 130 for all uses. In
comparison to the various studies carried out by EDF
R&D and current literature on the subject, in our opinion, this renovation project has the best performance in
the country in terms of energy eco-efficiency.
Conclusions
HDL wanted an exemplary refurbishment for its headquarters in terms of energy efficiency. This opera-
kWh/m2.year
4 000
6,0 Table 1. Comparison of consumption between the first
5,0 and second year of operation.
6,0
COP
6 000
2009/2010 : all uses consumptions
COP
8 000
kWh/Month
kWh/Month
8 000
2009/2010 : all uses consumptions
* : including the pump that
irriguates the probes
tion shows that we can, at reasonable costs (HVAC =
194 €/m²) reach less than 15 kWh/m².year for HVAC
and less than 25 including lighting. To achieve these levels of consumption on others operations, it will, whenever possible, be necessary to apply the eleven following principles:
• Insulate the walls at 0.25 W/m².K;
• Insulate the roof at 0.15 W/m².K;
• Install windows with Ug of 1.1 W/m².K,
preference for PVC;
• Limited the glazed surface to 30% of the vertical
walls;
• Systematize for lighting, the installation of T5
tubes with presence detection;
•Install a double flow AHU with rotary exchanger;
•Choose auxiliaries (pumps and fans) with variable
electronic speed;
•Install - the cornerstone of all - thermodynamic
machine with a COP close to 4 (water table or
vertical probes according constraints on site).
If these technical points are followed with these organizational measures:
• Regular controls on site during refurbishment
phase;
• Scrupulous (even zealous…) commissioning;
• Energy monitoring at the first start in winter,
• then, the renovation will, certainly, be a success.
REHVA Journal – January 2012
43